Image forming apparatus whose image bearing member is rotated by a pulley

Abstract

An image forming apparatus for forming an image on a recording material is constituted by an image bearing member, a driving source, a first pulley rotatable by actuation of the driving source, a second pulley, connected to a rotatable member, for transmitting rotation of the driving source to the image bearing member, a belt supported by the first pulley and the second pulley, a first pressing member which is disposed upstream from the first pulley with respect to a rotational direction of the drum and located closer to the second pulley than a rotation axis of the first pulley so as to press the first pulley through the belt, and a second pressing member disposed at a position substantially symmetrically opposite from the first pressing member with respect to a line connecting the rotation axis of the first pulley and a rotation axis of the second pulley so as to press the first pulley through the belt.

1. An image forming apparatus for forming an image on a recording material, comprising:
 an image bearing member; 
 a driving source; 
 a first pulley rotatable by driving power of said driving source; 
 a second pulley, for transmitting driving power of said driving source to said image bearing member; 
 a belt supported by said first pulley and said second pulley; 
 a first pressing pulley which is disposed upstream from said first pulley with respect to a rotational direction of said belt so as to press said first pulley through said belt, wherein a rotation axis of said first pressing pulley is provided between a rotation axis of said first pulley and a rotation axis of said second pulley with respect to a direction of a line connecting the rotation axis of said first pulley and the rotation axis of said second pulley; 
 a second pressing pulley disposed at a position substantially symmetrically opposite from said first pressing pulley with respect to the line connecting the rotation axis of said first pulley and the rotation axis of said second pulley so as to press said first pulley through said belt; 
 a first spring for pressing a first supporting member, for supporting said first pressing pulley, against said belt member so that said first pressing pulley presses said first pulley through said belt; and 
 a second spring for pressing a second supporting member, for supporting said second pressing pulley, against said belt member so that said second pressing pulley presses said first pulley through said belt, 
 wherein said first pressing pulley and said second pressing pulley press said first pulley through said belt at the same time so that a pressing force toward said first pulley by said first pressing pulley and a pressing force toward said first pulley by said second pressing pulley are canceled out with each other with respect to a direction perpendicular to the line connecting the rotation axis of said first pulley and the rotation axis of said second pulley. 
 
     
     
       2. An apparatus according to  claim 1 , wherein said first and second pressing pulleys increase a contact area between said first pulley and said belt. 
     
     
       3. An apparatus according to  claim 1 , wherein the rotation axis of said second pulley substantially coincides with a rotation axis of a rotatable member connected to said second pulley. 
     
     
       4. An apparatus according to  claim 1 , wherein said first and second pressing pulleys have a negative crowning configuration as a peripheral surface configuration. 
     
     
       5. An apparatus according to  claim 1 , wherein said first and second pressing pulleys are swingable with respect to a peripheral surface of said first pulley. 
     
     
       6. An apparatus according to  claim 1 , wherein said second pulley has an outer diameter larger than that of said first pulley. 
     
     
       7. An apparatus according to  claim 1 , wherein an angle formed between a line connecting rotation axes of said first pressing pulley and said first pulley and the line connecting rotation axes of said first and second pulleys is substantially equal to an angle formed between a line connecting rotation axes of said second pressing pulley and said first pulley and the line connecting rotation axes of said first and second pulleys. 
     
     
       8. An apparatus according to  claim 1 , wherein said image forming apparatus further comprises a first tension pulley and a second tension pulley which are disposed upstream and downstream, respectively, from said second pulley with respect to the rotational direction of said belt, each of said first and second tension pulleys being rotatable and configured and positioned to press said belt. 
     
     
       9. An apparatus according to  claim 1  wherein each of said first and second pressing pulleys is provided with an elastic member for pressing said first or second pressing pulley against said first pulley. 
     
     
       10. An apparatus according to  claim 1 , wherein said image bearing member is a photosensitive drum. 
     
     
       11. An apparatus according to  claim 1 , wherein said image bearing member is an intermediary transfer member for carrying a toner image. 
     
     
       12. An apparatus according to  claim 1 , wherein said first pressing pulley and said second pressing pulley press said first pulley through belt at the same time so that a pressing force toward said first pulley by said first pressing pulley and a pressing force toward said first pulley by said second pressing member pulley cancel out a tension of said belt with respect to a direction in which a rotation axis of said first pulley and a rotation axis of said second pulley are connected. 
     
     
       13. An apparatus according to  claim 6 , further comprising a first tension pulley and a second tension pulley which are disposed upstream and downstream, respectively, from said second pulley with respect to the rotational direction of said belt, each of said first and second tension pulleys being rotatable and configured and positioned separately from said second pulley so that neither said first tension pulley nor said second tension pulley press said second pulley through said belt.